1. Field of the Invention
The present invention relates to a polyester film for an image-forming transfer material. In particular, the present invention relates to a polyester film on which a high quality image is formed and from which the image is transferred to a receptor in a printing method which prints a full color image using an image-forming transfer material comprising a polyester film and a coloring light-sensitive layer formed thereon.
2. Description of the Related Art
There is known a printing method in which plural image-forming materials each comprising a polyester film and a coloring light-sensitive layer formed thereon are used, each image of yellow, magenta, cyan and black is formed on the respective image-forming material and then the image is transferred to a receptor to print a full color image on the receptor. Such method is preferably used in a color correction prior to real color printing. In such case, plural image-forming transfer materials are used to make one full color print, and positions of all the images relative to the receptor should be strictly adjusted. Otherwise, color deviation appears, so that the quality of the printed image is greatly deteriorated.
To overcome the above problem, it may be contemplated to precisely adjust the positions of the transfer sheets carrying the developed images of respective colors. However, when accuracy of positioning of the transfer sheets is mechanically improved, the color deviation may not be completely prevented, and in some cases, the color deviation which can be identified by eyes may appear.
Since a dimensional change of the substrate film of the transfer sheet has some influence on the color deviation, it is contemplated to suppress the color deviation by making the degrees of dimensional change of the substrate films same. That is, in the production of a biaxially oriented polyester film, the degree of dimensional change varies with a position in a width direction of the film because of bowing. Then, it is contemplated to use a center part of the film, or the same parts of the right and left edge portions of the film in order to suppress the color deviation. However, the use of the specific part of the film decreases the productivity, or the right and left parts can be confused, whereby the quality of the image is worsened greatly.